A poster child for India’s protracted development cycles, the Tejas Light Combat Aircraft project was undertaken in 1983 by Hindustan Aeronautics Ltd., and the aircraft is not yet fully operational. (ADA photo)

An article in Sina's Chinese-language military news web portal compared the abilities of India's HAL Tejas Light Combat Aircraft and the FC-1 Xiaolong/JF-17 Thunder developed jointly by China and Pakistan.

Overview of the Aircraft

The HAL Tejas Light Combat Aircraft (LCA) was named by former Indian prime minister Atal Bihari Vajpayee. The development plan was approved by the Indian government in 1983. The government's requirements for the Tejas were to develop an all-weather supersonic LCA which could replace the MiG-21. Its main mission is to fight for control of airspace and to offer short-range support. The development of the Tejas wasn't a simple process, as it included a completely new engine, avionics and weapons systems, in line with global standards. The first test plane was unveiled on Nov. 17, 1995 and made its maiden flight on Jan. 4, 2001.

The design for the PAC JF-17 Thunder, also known as the FC-1 Xiaolong, began with the "Super 7" plan launched jointly by China and US aircraft maker Grumman to develop an upgraded version of the F-7, but Grumman left the project after sanctions were placed on China by the US in the wake of the Tiananmen Square Massacre in 1989. China and Pakistan subsequently signed a memorandum of understanding to design a new fighter together in 1995. The requirements for the fighter were that it make use of advanced technology, that it be a completely new design and that it approach the combat capabilities of third-generation fighters. It also needed to be light, cheap to produce and capable of carrying a large payload. The first plane took its maiden flight in 2003 and the third aircraft made a successful test flight in April of 2004. In the same year, the state-owned China National Aero-Technology Import & Export Corporation (CATIC) and the Pakistan Air Force signed a contract for the production of the FC-1 Xiaolong/JF-17 Thunder, the new designations of what had been the Super 7. On April 28, 2006, weapons systems and avionics were installed in the fourth aircraft and it made a successful test flight. The avionics systems were developed by China. On Sept. 10, 2006, the sixth JF-17 made its maiden flight.

Aerodynamic Configuration

There are clear differences in the shape of the two planes. The Xiaolong has horizontal tail-planes and a conventional aerodynamic structure, while the Tejas has no horizontal tail-planes on its triangular structure.

The lack of a (horizontal) tail is a unique feature of the Tejas, making it similar to the Dassault Mirage series of fighters. The plane also has a delta-wing configuration, which is the reverse of normal delta-wing fighters in that the angle of the sweep of the outer wing section is larger than the angle of the sweep of the inner wing section. The reverse configuration is normally used to balance supersonic and subsonic or transonic capabilities. The Tejas has an angle of incidence from the main axis of the wing, which gives the whole plane a larger dihedral force, improving its supersonic capabilities.

The Xiaolong has a trapezoid-shaped wing configuration, with a larger wing-aspect ratio and a smaller induced drag, therefore at high-altitude subsonic speed, the entire plane has a higher lift-drag ratio. The large wings that extend to the inlets on both sides of the plane's body not only improve the aircraft's lift during high-angle-of-attack flight but also help improve the maneuverability of the plane. The eddies created during high-angle-of-attack flight are also relatively stable, which reduces the chance of sudden drops in lift and improves the balance of the plane. It also improves the directivity of the nose of the plane in close-range combat.

In summary, in conventional air warfare, at an altitude of around 8,000 meters and a speed of Mach 0.8-1.2, the Xiaolong performs better in terms of acceleration, climb, stability and other combat capabilities. The Tejas' advantage lies in its low wing aspect ratio and its relatively low wave drag, which makes it superior to the Xiaolong in supersonic conditions.

Inlet Design

Both planes have intake cowls on both sides, but the Xiaolong's design is better as it is more functional, improves the plane's stealth capabilities and reduces its weight.

The Tejas uses the V-shaped air inlets typical of light fighters, the air inlets gather together towards the rear, sheltering the blades of the engine's axial compressor, preventing the scattering of radar, and adding to the craft's stealth capabilities. The oval air intakes are similar to the F/A-18C/D Hornet, with a diverter structure around them. All in all the design is in line with convention and has not shown much innovation.

The Xiaolong's air intake design is a little more imaginative and more advanced. It uses a diverterless supersonic inlet (DSI), scrapping the diverter structure used around the air intakes, as well as the air bleed and air bypass structures of most conventional supersonic aircraft. Through use of a three-dimensional compression surface to divert the boundary layer airflow at high subsonic and supersonic speeds, there is no longer a need for supplementary air inlets or bleed doors. This has the effect of lightening the structure, reducing drag and radar return. The air inlets are forward sweeping in a ramp formation, which reduces wave drag or surface interference.

Materials

As the Xiaolong was developed exclusively for export, to control costs, its body is mainly constructed with aluminum alloy as opposed to more popular composite material. The Tejas, however, has put an emphasis on reducing weight, and so it has used a lot of composite material. Forty-five percent of the plane's total weight is comprised of composite materials, including the fuselage, its vertical tailfin, the skin, the spars and the ribs of the wings, the elevons, the rudder, the air brakes and the landing gear doors. This cuts the plane's empty weight by 5.5 tons, making it almost 1 ton lighter than the Xiaolong, which means it can carry more fuel and a heavier load. The plane has a cargo-internal fuel ratio of around 30%, which improves its combat abilities.

Propulsion Systems

Although the Tejas' F414 engine is superior in terms of functionality, durability and life span to the Xiaolong's RD93 engine, it is also more expensive.

The choice of an engine has been problematic in the development of both aircraft. Those developing the Xiaolong had the choice of the commonly used F404, Pratt & Whitney's PW1216, the Turbo-Union RB199, the Snecma M88 and the Russian RD33. After considering different parameters, such as the combat radius, external storage and flexibility, they chose the RD-93 afterburning turbofan due to its low fuel uptake and its reasonable price.

The RD-93 is a variant of the RD-33 developed specifically for the Xiaolong, the main changes being the repositioning of the gearbox along the bottom of the engine casing and its mechanical turbine control. It employs a four-stage fan and nine high pressure stage compressor, with military thrust of 50 kiloNewtons (kN) and 81.3 kN thrust with afterburner, an augmented thrust ratio of 1.628, an overall pressure ratio of 21:1, a bypass ratio of 0.48:1, a normal gross takeoff weight of 9.1 tons and a thrust-to-weight ratio of 1, which gives it a longer range and better flying and propulsion capabilities.

The original plan for the LCA Tejas was that it would be fitted with the GTRE GTX-35VS Kaveri turbofan engine, but the development of the engine ran into a hitch, so they had to adopt the F414 instead. The engine was developed on the basis of the General Electric F404 and has an axial compressor with three fan and seven compressor stages and a turbine with one low-pressure and one high-pressure stage. Compared with the F404, the F414 has augmented thrust by 35%, pushing it to 60 kN military thrust and 98 kN with afterburner. Its thrust-weight ratio has been pushed to 9:1. India purchased the custom-made F414-GE-INS5 model, which has similar capabilities to the F414-GE-400, with a fully digital control system, more advanced than the RD-93's mechanical turbine control, making it quicker to react and more accurate.

Like the Tejas, the FC-1 Xiaolong was intended as a low-cost fighter and was jointly developed by China and Pakistan, although the extent of the latter’s contribution remains unclear. (Chinese Internet photo)

The F414 engine has an advantage over the RD-93 engine, as its technology is more advanced; it has greater thrust and is more reliable. The RD-93 was designed in the 1970s and is a little past its best in terms of design, but it does offer more stability, a better price and a high quality-price ratio. However, the Xiaolong will likely adopt the Chinese WS-13 engine in the future. The WS-13 is an improved version of the RD-93 engine, with a better design and more attention to materials and details in its production. It also uses the full authority digital engine control (FADEC) system, which creates the possibility that it may be smaller than the F-414.

Avionics and Flight Control Systems

The LCA Tejas' avionics system has a top-down design and has made use of line-replaceable unit technology, ensuring smooth coordination and the minimum degree of interdependence. The Tejas' avionics system was designed by France, with three 1553B serial buses and two centralized 32-bit, high-throughput mission computers, including a communications subsystem, a mission subsystem, a self-defense system and a guidance and flight system. It uses ELTA's EL/M2032 radar system, which works in the X-band range, designed for both air-to-air and ground strike missions. It is effective within a range of 37-75 km.

The Xiaolong's avionics also have a top-down design, with an onboard computer and a 1553B serial bus at the center, integrating several systems, including the cockpit display and control system, task management systems and fire control systems. It is equipped with autonomous navigation technology and can attack land, air and sea targets, tracking while scanning. If the users can afford it, it can also be equipped with globally competitive avionics systems. It can be equipped with the KLJ-7 X-band fire and control radar, for example, which has 14 air-to-air and air-to-ground modes, and can follow 10 targets while in track and scan mode. It can also unleash an attack at two targets simultaneously. Its mid-range guided missiles can also hit targets beyond visual range. For targets of 5 meters squared, its range in look-down search mode is 105 km and 85 km in look-down mode.

Chinese avionics have come a long way in recent years and even in comparison with the Western avionics system used in the LCA Tejas, it doesn't lose out in terms of capability and its search range is greater and functionality greater than that of the Tejas.

Flight Control Systems

The flight system of the Tejas has a more complicated origin. Originally the aircraft was set to be equipped with a FADEC system developed jointly by Lockheed Martin and India, however, an Indian nuclear test led to sanctions being implemented against the country, ending the US-Indian cooperative endeavor. India then looked to Russian aircraft manufacturer Mikoyan and Moscow Air Production Organization for help, until the sanctions were revoked in 2001. India then ordered actuators from London-based BAE Systems, which were handed over in 2003. Then Lockheed Martin joined the development project once again. This lengthy process slowed down the entire development of the aircraft. Overall, the core parts of the system were completed by Lockheed Martin, although this information has yet to be released to the public. The Indian media have reported that the flight control system is a match for the F-16C/D Fighting Falcon's relaxed static stability/fly-by-wire flight control system.

The Xiaolong's flight control systems make use of a longitudinal FADEC system, with two fly-by-wire back-up systems. The FADEC system improves stability across the yaw and roll axis. It has overcome a few flaws in its aerodynamics to allow for more maneuverability. It is also relatively low in price.

Combat Ability

There is no real competition between the two aircraft in terms of combat ability. The Xiaolong has already completely developed its combat capabilities, with the ability to fire radar-guided air-to-air SD-10 missiles, air-launched C-802AK anti-ship missiles and precision bombs. The LCA Tejas, on the other hand, has just entered service, so it hasn't developed its combat abilities as yet, so the only way to compare the two is to look at the weapons they will likely use and their weapon pylons.

Those behind both the Tejas and the Xiaolong demanded comprehensive combat capabilities for the two fighters, to allow them to use a diverse range of weaponry. The fixed weapon on both fighters is a double-barreled 23 mm aircraft gun. The difference between them is that the Tejas' gun is sourced from Russia, whereas the Xiaolong uses China's variant of the gun. The LCA has eight weapon pylons on the entire plane, with three under each wing, one under the central body of the plane, and one under the air inlets on the left side of the plane. This allows the plane to make use of a wide range of the weapon systems of the Indian Army. This includes mid and close-range air-to-air missiles, precision-guided weapons, air-to-surface (including anti-ship) missiles, conventional and retarded bombs, cluster bombs and unguided rockets. The pylons can carry a maximum weight of 4 tons. The Xiaolong has 7 external pylons, two at the tips of the wings, four under the wings and one on the belly of the fuselage. This allows it to carry the beyond-visual-range radar guided SD-10 missile and the PL-9 short-range, infrared-homing air-to-air missile, as well as air-to-surface missiles, such as anti-ship and anti-radiation missiles, laser-guided bombs, anti-runway penetration bombs and cluster bombs. It can also carry three high-capacity subsidiary oil tanks. It can carry a total of 3.6 tons externally.

The two fighters are aimed primarily at air-to-air combat, while still maintaining ground strike and anti-ship attack capabilities. The Xiaolong will likely carry two PL-5EII air-to-air homing missiles, two SD-10 mid-range air-to-air missiles and two or three subsidiary oil tanks in its standard configuration. When engaging in beyond-visual range combat, it will likely carry four SD-10 missiles. The LCA Tejas will likely be equipped with the Israeli Python-4 air-to-air missile and the Derby medium-range active radar homing missile. The Python-4 approaches the PL-5EII in terms of its capabilities, but the range of the Derby missile is a lot shorter than that of the SD-10, so the Xiaolong has the advantage in terms of beyond visual range combat.

Overall, the LCA Tejas and the Xiaolong are matched in terms of their weapons pylons and as India's own weapon production abilities are quite limited, the LCA Tejas makes use of mainly Western and Russian advanced weapon systems, which makes for a scattered weapon set, which is more challenging for the pilot to manage. The Xiaolong's weapon systems and nacelle are all designed by China, which makes for more coordination between its weapons systems and a good price-to-quality ratio, which is a big advantage for the Xiaolong.

Conclusion

The Tejas is a light multirole fighter fit for the 21st century. It uses a lot of new technology and innovation, such as its use of large amounts of composite materials, its advanced avionics system and its unique aerodynamic configuration. In terms of functionality, the LCA Tejas has good potential to be expanded into variants. For example, at a time when the air force version is yet to be commissioned widely, a ship-based version of the aircraft has already been released. The Xiaolong is a third-generation model designed for the international market. The use of off-the-shelf materials not only cuts costs but also reduces risks in the design process and improves the reliability of the aircraft. This will not make it the best aircraft, but rather a standard, cheap and reliable model for air-to-air combat. In summation, the Xiaolong is the aircraft of today and the Tejas is the aircraft of tomorrow.